1. Field of the Invention
The present invention relates to a magnetic head and, more particularly, to a magnetic head having a magnetic core in which a magnetic film made of a material having a high saturation magnetic flux density is formed on a block made of a material of high permeability.
2. Related Background Art
In VTR (video tape recorders) using a magnetic tape of a width of 8 mm as a recording medium and electrophotographic cameras which have recently been developed, a medium having a high coercive force Hc of 1300 to 1500 Oe such as the so-called metal powder medium or the like is used as a recording medium.
Therefore, in the conventional magnetic head using only a ferrite system material as a magnetic core material, the saturation magnetic flux density Bs of the magnetic core is at most about 5000 gauss. Thus, if a material having a high coercive force is used for the medium saturation of the magnetic core will occur, reducing the recording efficiency.
To prevent this, a magnetic head in which a magnetic alloy such as Sendust, amorphous, or the like having a high saturation magnetic flux density is used as a magnetic core material. However, in the case of manufacturing the magnetic core of such a head, it is a fundamental technique to form the magnetic core by joining the chip-like core half bodies through the magnetic gap so as to face each other. Therefore, in this case, several problems arise such that the mass productivity is low and a variation in characteristics is large, so that the manufacturing costs remarkably increase as compared with the method such as in the ferrite cores whereby after abutting blocks, they are sliced to obtain a number of cores.
To solve the problem of the mass productivity, there have been proposed various kinds of what are called composite type magnetic cores in which the foregoing magnetic alloy material is used for the abutting surface portions which sandwich the magnetic gap between the core half bodies and ferrite is used for the remaining portions.
The magnetic head having such a structure is called MIG (Metal In Gap) head and has already been put into practical use.
The MIG head has the structure such that almost all of the core portion is made of a material of high permeability such as ferrite or the like and the magnetic pole edge portion near the gap is made of a material of high saturation magnetic flux density, namely, as alloy magnetic material such as permalloy, Sendust, amorphous, or the like. The MIG head includes two types: the type in which the boundary between the metal magnetic material and the ferrite on the slide surface is parallel with the operating gap (this type is called P type; for example, the P type is disclosed in the Official Gazette of Japanese Patent Unexamined Publication No. 140708/1976, and the like); and the type in which the boundary is not parallel with the operating gap but has an azimuth (this type is called A type; for example, the A type is disclosed in the Official Gazettes of Japanese Patent Unexamined Publication Nos. 96013/1979, 32107/1985, and the like). The MIG head of the A type has already been put into practical use. This is because according to the MIG head of the P type, the boundary between the metal magnetic material and the ferrite functions as a pseudo gap and a ripple voltage of about a few dB as the peak-to-peak value appears in the frequency to output characteristic by the contour effect due to the function of the pseudo gap.
However, in the foregoing MIG head, the operating magnetic gap is formed by the so-called abutting process. In heads in which the operating gap is formed by the conventional abutting process, the gap width varies greatly, resulting in greater variations in the characteristics of the heads.
In particular, in the case of the core for use in the 8-millimeter VTR, the track width is extremely narrow (about 15 .mu.m) and the gap width is very narrow (about 0.25 .mu.m). Therefore, in the abutting process, extremely high degrees of accuracy are needed to accurately position the tracks and to form the gap, and fairly large variations in dimensions of the track and gap occur. Even if a desired gap width assumes, for example, 0.25 .mu.m, it will vary within a range of about 0.2 to 0.3 .mu.m.
This results in a deterioration of the yield.
To solve this problem, a method of manufacturing the magnetic core in which the abutting process is eliminated has been proposed. FIGS. 1A to 1D are diagrams for explaining an example (Japanese Patent Unexamined Publication No. 73913/1980) of the manufacturing method.
First, a through hole 2 to wind a winding is formed in a core base plate 1 as shown in FIG. 1A. A core half body 3 consisting of a film of Sendust alloy or the like is formed on the core base plate 1 by a sputtering method or the like as shown in FIG. 1B. A nonmagnetic gap material 4 such as SiO.sub.2 or the like of a predetermined thickness is deposited on the surface of the core base plate 1 where a magnetic gap will be formed. Next, after a ferromagnetic material such as Sendust alloy or the like is deposited on the core base plate 1 by the sputtering method or the like as indicated by an arrow A in FIG. 1B, the magnetic material deposited on the unnecessary portions is removed and the film of the remaining magnetic material as shown in FIG. 1C is used as a second core half body 5, so that a magnetic core as shown in FIG. 1C is derived.
Although the magnetic core manufactured by this method doesn't have the foregoing problem due to the abutting process, another problem occurs.
Namely, the through hole 2 needs to be formed in the core base plate 1. On the other hand, in the case of forming the azimuth in the magnetic gap, a fixed azimuth angle .theta. must be formed by the gap forming surface B of the core half body 3 as shown in FIG. 1B. Further, when the magnetic material film of the second half body 5 is formed, as shown in a cross sectional view of FIG. 1D, if a film is formed on the surface having a stairway portion, the characteristic of the magnetic material will deteriorate near the edge portions C and D where the surfaces cross with each other.
According to this manufacturing method, it is extremely difficult to cheaply manufacture the cores without encountering those problems.
The applicant of the present invention has already proposed the manufacturing method whereby the abutting process is omitted and the mass productivity can be further improved in consideration of the above point. FIGS. 2A to 2H are diagrams for explaining this manufacturing method.
First, a block 6 made of a magnetic alloy material of high saturation magnetic flux density such as Sendust or the like as shown in FIG. 2A is prepared. A winding window 7 is then formed into the block 6 by digging, grinding, or the like as shown in FIG. 2B.
Next, as shown in FIG. 2C, the winding window 7 is embedded with a cover material 8 such as aluminum, silver solder, or the like. Further, a nonmagnetic material of SiO.sub.2 having a predetermined thickness is deposited as a magnetic gap 9 onto the magnetic gap forming surface of the block 6 by the sputtering method or the like.
Next, as shown in FIG. 2D, a magnetic material film 10 such as Sendust or the like is deposited as a core by the sputtering method or the like so that the magnetic gap 9 is sandwiched by the film 10 and the block 6.
Subsequently, as shown in FIG. 2E, the cover material 8 is dissolved again exposing the winding window 7.
Further, as indicated by an alternate long and short dash line in FIG. 2F, the resultant whole assembly is cut at the azimuth angle .theta..
FIG. 2G shows a state in which a reinforcing plate 11 of a nonmagnetic material is adhered onto the cut surface by an adhesive agent 12. The resultant assembly is further cut along an alternate long and short dash line shown in FIG. 2G.
A reinforcing plate 14 of a nonmagnetic material is also adhered onto the cut surface by an adhesive agent 13 as shown in FIG. 2H, thereby obtaining a magnetic core.
Although the mass productivity is remarkably improved according to the manufacturing method shown in FIGS. 2A to 2H as compared with that by the manufacturing method in FIGS. 1A to 1D, the former method still has the following problems.
First, as shown in FIG. 2H, two reinforcing plates 11 and 14 need to be adhered with respect to one magnetic core. In addition, the thickness of the magnetic material film 10 (in the sliding direction of the medium) needs to be set to about 0.5 mm, which is equal to the dimension from the medium slide surface to the upper end of the winding window 7 in terms of the characteristic of the core. However, it takes tens of hours to form the film of a thickness of about 0.5 mm by the physical evaporation deposition such as the sputtering method or the like, thereby reducing productivity. If the film thickness is set to a small value, on the contrary, the resistance of the magnetic circuit will increase and the output will decrease.